Just musing as I digest lunch here - I have often wondered how much of the
"ringing" we hear in filters is a psychoacoustic effect. Bear with me a
moment... In using my NIR-12 I can select center frequency and width. I
notice that when the width is narrowed around a marginal (i.e. in the
noise) signal, I have more difficulty distinguishing the signal from the
noise. Sometimes, the narrower the bandwidth, the more difficult to hear.
I think there is something going on in the ear/brain connection that allows
us to integrate out the noise better when it is broadband, but when the
noise bandwidth is narrower, it's harder for us to distinguish the signal
in the noise against it.
Of course, filters do ring (some a lot, some a little), and the amazing TT
250 Hz filter somehow decreases noise compared to the signal, so there are
exceptions to this. But, after playing with DSP's so much for a couple of
years, this really intrigued me.
73, Duane AC5AA (lunch is over, the blood has been diverted to the
midsection, brain functions cease....)
Duane A. Calvin
Server Systems Test Engineer
Dept. 76TS RS/6000 - SP Nodes
IBM Austin, TX >O< Tie: 793-3368
Clark Savage Turner <csturner@falcon.csc.calpoly.edu> on 10/27/99 10:16:10
AM
To: "Dr. Gerald N. Johnson, P.E." <geraldj@ames.net>
cc: W8JI@contesting.com, tentec@contesting.com
Subject: Re: [TenTec] Ten-tec noise and RX questions
On Wed, 27 Oct 1999, Dr. Gerald N. Johnson, P.E. wrote:
> 3. Tentec filters ring a lot less on tropical noise than most other
> filters. I've not used the narrow CW filter but have no problems with
This is a topic I am very interested in. I have put an INRAD
400 Hz (lattice design) and NS (Ten Tec) 500 Hz (ladder design)
filter in my rig's 9 MHz first IF to see if I could detect a
difference in the ringing. These are both, of course, behind
the INRAD 2.8 filter as the main filter in line all the time.
There was little detectable difference. The Ten Tec filter seemed
to be centered differently, so more high frequency ringing went on.
The 400 Hz seemed to ring a little lower in frequency. They both
made extra noise to my ears.
However, the Ten Tec 221, the little 250 Hz ladder filter with
500 Hz center was like magic. The noise almost disappears when
I hit the button. Really big difference, really increases my
ability to hear things. However, it is lossy, and some weak
signals will drop below the AGC threshold and I need to work
the gain controls to try to hear them. Overall, a wonderful
filter to have in there. For 160 atmospherics, this might be
the filter to have. I have yet to work it down there, hoping
to put up a 160 antenna in the next two weeks.
Clark
WA3JPG
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